HYDRAULICS BRANCH

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EYJRhUL!C LABORATORY

NOT 'i"O BE Ei::.11CVED J.'ROivl FILES

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UN I TED SH :ES

DEPARTME�T OF THE INTERIOR

BUREAU OF RECLAMATION

HYDRAULIC LtBORfTORY REPORT �O. 153

hODEL STUDIES OF THE l�ITlfL

REG' LftTION OF FLOW tT t�DERSO� R�NCH DPM, SOiSE PROJECT

3y

FRED LOCHER. flSS0Cl�TE ENG!NEER

De�ver, C0lorarlo Seoter,ber L6, 1944

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UNITED STATES DEPARTMENT OF THE INTERIOR

BUREAU OF RECLAMATION

Branch of Design and Construction Engineering and Geological Control and Research Division

Denver, Colorado Septenber 26, 1944

Laboratory Report No, 153 Hydraulic Laboratory

Compiled by Fred Locher Reviewed by J. E. Warnock

Subject: Model studies of the initial regulation of flow at Anderson Ranch Dam - Boise Project, Idaho.

1. The original design of the penstock at Anderson Ranch Dam

provided for the flow of water to the turbines and to a branching

line which lead to four 72-inch hollow-jet valves, At the reser­

voir end of the.penstock a bulkhead-type gate was provided to allow

for u:mvateri ng the pens tock when necessary. The hollow-jet valves

would have provided for passing discharges up to 10,000 second-feet.

Larger flows which could not be stored in the reservoir would have

been discharged over too spillway. Due to the present emergency, it

was not possible to obtain the valves and to regulate the flow ac­

cordingly. To conserve water and later pass it downstream to the

power plants during the dry season, it was necessary to change the

bulkhead gate to a regulating gate and operate the penstocks as ordi­

nary outlets through the dam o

2. The regulation of flow with the temporary arrangement was

expected to begin in 1944, at which time it we.s expected that the

?rater level in the reservoir wouln be at elevation 4050. During the

1944 season e.nd part of the 1945 season the revised gate at the pen­

stock was to be used for regulation of the flowo At some time during

1945 it was expected that the reservoir would have stored sufficient

water to raise the. level to plus or minus 4105, thereby creating suf­

ficient head to make it impractical to use the gate as a regulating

device. At thi t'l point it was planned to place one of the 84-inoh

Boulder needle valves in the conduit for the regulation of flow and

the slide gate was to be returned to its original use as an emergency

bulkhead.

3. The use of the gate as a regulating device presented a prob-.

lem in cavitation which was further complicated by the fact tm.t at

no time during the release of water by. this method was the oondui t ex­

pected to flow fullo Further, the intake was considerably above the

horizontal part of the conduit (figure 1), which would ne oeasi tate two

sharp turns in the flow before it reached the outleto It was expected

that this turning of the flow in the upper reaches of the conduit

would cause parts of the conduit to becolll8 filled near the intake, with

the result that severe subatmospheric preasurea and the resulting pit­

ting would be obtainedo

4o A 1:40 hydraulic model was constructed to determine the oapac -

ity of the air vents and a suitable location for themo Preliminary ·

tests with the arrangement shown on figure l indicated that satisfac--.'.!: .

tory operation could be obtained by connecting an air-vent pipe be­

tween the penstock immediately downstream from the 46-degree bend and

the upstream end of the transitiono As the horizontal part of the

penstock did not flow full. the vent pipe would have allowed air from

this region to flow into the cavity formed in the transition and would

prevent any severe subatmospherio pressures 0

5. The intake center line of this scheme was at elevation

3969.16 (figure l)o As several earth s lides in the reservoir area of

the prototype have already occurred, it appeared advisable to raise

the intake to elevation 4000000 to eliminate the danger of clogging by

some future slide or submerged trasho

6. In the new arrangement the center line of the intake was

placed at elevation 4000000, e.nd the connection to the present instal­

lation was effected by a vertical drop "t9 a 90-degree bend at the be­

ginning of the horiiontal part of the penstock (figure 2). The first

test with this arrangement showed th.at the water flowing under the gate

2

continued across the vartioal section of the conduit and was deflected

back and forth across the conduit as it dropped down to the horizontal

section, causing a siphon action which would have lowered the pressures

in the prototype to the vapor pressure Qf watero These pressures were

relieved, and the siphon action was partly broken by placing a l50-inch

air vent in the top of the transition downstream from the gates h<JW­

ever, the pressures on the bottom of the transition were still suffi­

ciently low to cause pittingo This oondition was remedied br placing

a step and another vent in the transition and also clanging the former

l50-inch vent to 20 inches in diameter {figure 3) o

7 o With this arrangement it would m ve been necessary to remove

the step when conditions made it unnecessary to use the gate as a

regulating device o To overcome this objection the step was changed to

a recess (fieure 3) having the same vent �stemo This scheme was

tested for regulation of flow with the gate and under the normal oper­

ating conditions of the completed projecto There were no negative

pressures for normal operationo The recess and the vents did not have

any adverse effects on the flows, indicating that it would not be ne­

cessary to fill or plug them after they had served their purpose. Some

negative pressure, still prevailed when the gate was used as a regulat­

ing device, however, they were not serious enough to warrant the addi­

tional cost to alleviate them, inasmuch a s the arrangement was to be

temporaryo The piezoiretric pressures converted to p_rototype, for aera­

tion with the step and the. recess, are shown on figure 4o They apply

when the gate is used for regulating the flow.

DISCHARGE C . F S.

IO 4 0 0 - ----- -- -

8000

5880

4000

IO I 7 0

8 2 00

6080

4000

3 2 5 0

DISCHARGE C.F. S.

IO 2 7 0

8800

8 2 00

6070

3745

10 5 9 0

81 00

5 980

32 40

HEAD ON i GATE

FT WATER

I 02 . 0 �---- -

IO 2 . 5

IO 2 . 4

IO 5. 5

4 9. 7

5 I. 7

4 9. 3

5 0 . 8

49. 8

----

-

I

-6.0 ----

- 8. 8 - -- -

-8.4 -- --

-4. 6

- 9.0 ..

- 2 .4 -

- 3. 2

-7.4

- 3.6

.-- ·- --

2

39. 2 ---- --

4.6 -------

5 2 . 4 - -·

60. 8

12 . 0

18 .0 fL----

2 I. 6

28. 0

2 8. 8

PIEZOMETER NUMBER - -

3

4.0

3.6 ,__ _____

14.4

20. 0 - --·- -

- I. 40

I. 00

2 .80

6.40

10.8

-

4

4.0

- 1 .6 -· -·

- 8. 0

-5.6 -- -

3.8

3.4

I. 8

- 1 .4

- -- --

- .20

- -

5 6

- 1.6 -14.6 ----

-5.2 - 12 . 0

-8.0 - 8. 9

-7.2 -

- 1 .2 -

- I. 2 -

-2.4 -

- 4.4 -

- 4.0 -

7

-13. 6 -

- 11 . 6

- 8. 4

- 4.4

-12 .0

- 8.8

- 7. 6

- 4.0

- 2 . 8

PIEZOMETRIC PRESSURES FOR DESIGN 2 (Step in bottom of transition)

HEAD ON PIEZOMETER NUMBER i GATE

FT. WATER I 2 3 4 5 6 7

I 04. 0 17.8 -0.4 38. 8 0.6 - I. 8 -8.4 -12 . 2

IO 2 . 5 19.8 - 2 .0 43. 2 3.0 - I. 8 - 6.2 - 6. 2

IO 3 . 2 20. 6 - 1.2 50.4 5.0 - I. 2 -6. 2 - 6. 2

I 06. 6 25. 0 -7.4 5 7. 6 - 4.6 - 6.6 -4. 2 4.8

I 02 . 0 3.8 - 1.2 20. 4 -15.2 - 4. 8 0.0 0.0

48. 9 8.2 1 .6 8.8 - 0.6 - 0.2 - 5. 0 - 8. 0

48. 4 9.8 0.4 14.8 - 0.2 -0.2 -4. 0 - 6.4

5 5 . 6 I I. 2 - 1.8 26. 2 3.4 - 0.6 -2 .4 - 0.4

4 7. 2 1 1 . 0 - 2 .4 27. 2 9.0 7.0 - 2 . 0 - I. 4

PIEZOMETRIC PRESSURES FOR DESIGN 3 (Recess in bottom of transition)

Note: For piezometer locations see figure

...

·--

8

-4.0

- 4.0

- 1.0

-4.0 ·-

-4.5

- 3.0

0.0

0.2

0.2

8

-10. 4

- 10. 4

- 9. 4

- 8. 2

0.0

- 4. 2

- 5. 0

- 4.0

0.0 '1-i q:; �